The aim of this proposal is to study important aspects of the metabolism of leukocytes, namely factors which regulate the stimulation of these cells. Phagocytes are stimulated by a variety of agents, including microorganisms, mediators of inflammation, and immune complexes. The mechanisms by which stimulation of neutrophils are regulated are incompletely understood. Therefore, it is important to develop an understanding of the factors involved so that adverse effects which may occur during inflammation may be better controlled and insufficiencies of neutrophil function might be positively modulated. In this grant, experiments are proposed utilizing both biochemical and structural approaches which are directed toward elucidation of events related to neutrophil stimulation. We will study cell stimulation using retinoids as stimuli. These agents have interesting properties which make them useful tools for the study of different aspects of the stimulatory process. We will also utilize synergistic conditions of stimulation (i.e., combinations of low levels of stimuli which alone do not stimulate) to study this process since it is felt that these conditions may be more reflective of the situation in vivo than stimulation by high levels of a single stimulus. Novel secretory compartments have recently been implicated in early events associated with neutrophil stimulation. The presence and organization of these organelles, as well as their behavior during stimulation, will be assessed using structural and biochemical techniques. Membrane dynamics during stimulation will be studied; the distribution of C3b receptors will be used as a probe in these experiments. Additionally, the distribution of these receptors will be compared in resting and stimulated neutrophils. Alterations in the cytoskeleton of neutrophils (i.e., transient increases in F-actin) have been noted by others in the case of stimulation with chemotactic peptides. We have evidence suggestive of prolonged increases in F-actin with certain stimuli (e.g., retinoids). Furthermore, retinoids can alter the pattern of stimulation observed with other agents (e.g., chemotactic peptides). We will determine the effects of retinoids, alone or in combination with other stimuli, on the cytoskeleton by biochemical and cytochemical means. In summary, these experiments will utilize cell biological and biochemical approaches to develop a better understanding of the process involved in neutrophil stimulation.